In the 18th Century smallpox was a major killer.
Lady Mary Montagu learnt about inoculation in Turkey (it was introudced in Turkey and China) and introudced it to Britian.
She discovered that a healthy person could be immunised against smallpox using pus from the sores of someone suffering
A thread soaked in pus was drawn through a small cut in the person to be inoculated . After a mild reaction, they were immine to smallpox.
Unfortuantly inoculation sometimes led to full blown smalpox and death. The fear of smallpox led people to take the risk of inoculation. Many doctors became rich doing this.